Considerable research has been conducted regarding the binding of monoclonal antibodies (mAbs) to tumor-associated cell surface antigens. The preferential expression of tumor antigens by neoplastic cells allows the antigens to be used as diagnostic and therapeutic tools, as discussed generally in Hellstrom et al., Accomplishments in Cancer Research, 1984 Prize Year, General Motors Cancer Foundation (Fortner and Rhoads, eds.), pp. 216-240 (1985); and Reisfeld et al., Monoclonal Antibodies and Cancer Therapy, UCLA Symposia on Molecular and Cellular Biology, New Series, Vol. 27 (1985).
Previous research has shown that IgG.sub.2a and IgG.sub.3 antibody subclasses hold particular promise in tumor therapy since they are capable of mediating antibody-dependent cellular cytotoxicity (ADCC) in the presence of lymphocytes or complement. For example, use of these subclasses of antibodies to mediate ADCC has been demonstrated in human tumor-bearing nude mice and rats, and in human cancer patients as described in Sears et al., Lancet 1:762-765 (1982); and Houghton et al., Proc. Natl. Acad. Sci. USA 82:1242-1246 (1985).
The present invention involves in part a monoclonal antibody designated as "L6," which is an immunoglobulin type IgG.sub.2a. The L6 mAb has been shown to bind to a surface epitope of human lung, colon, breast and ovarian carcinomas, as well as melanomas. Hellstrom et al., Proc. Natl. Acad. Sci. USA 83:7059-7063 (1986). Hence, L6 holds particular promise for tumor therapy and diagnosis, particularly since it exhibits the ability to "target" certain cells, including neoplastic cells, and the apparent ability to manifest ADCC oncolytic activity in rodents. Id.
The present invention as described herein involves the discovery, isolation, and characterization of a specific antigen to which the L6 monoclonal antibody binds.